THE SEQUENCE OF THE HAEMOPHILUS-INFLUENZAE MUTB GENE INDICATES IT ENCODES A DNA HELICASE II-LIKE PROTEIN

A 6.2-kb Haemophilus influence genomic DNA fragment which partially co mplemented both the mutator and ultraviolet light sensitive (UVS) phen otypes of the H. influenzae mutB1 mutant was isolated. This fragment w as also able to complement the UVS phenotype of Escherichia coli uvrD mutant hosts. The uvrD(+) gene complemented the mutator phenotype of m utB1 hosts. The nucleotide (nt) sequence of the 6.2-kb fragment reveal ed an open reading frame (ORF) of 2184 bp. This ORF shows similarity a t both the nt and amino acid (aa) levels with the uvrD D gene of E. co li. Comparison of the sequences revealed eight regions of aa conservat ion in addition to seven previously identified helicase superfamily do mains. The nt sequence 5' to the mutB ORF contains several potential r egulatory motifs, including a LexA-binding site. Based upon these obse rvations, we are confident that the mutB gene of H. influenzae encodes an ATP-dependent DNA helicase-like activity.